JPS61120015A - Ultrasonic flow meter - Google Patents

Abstract

PURPOSE:To take an accurate measurement even if the temperature of fluid varies by detecting the temperature of the fluid from the propagation time of an ultrasonic wave which is propagated without passing through a flow of the fluid and determining the quantity of correction, and correcting a calcu lated flow rate by using the propagation time difference. CONSTITUTION:An ultrasonic wave radiated by one of ultrasonic oscillators 1 and 1' crosses a pipe 4 in which the fluid 3 flows at a specific angle and is reflected by the internal wall of the pipe 4 reaches the other at a specific angle. For the purpose, the oscillators 1 an 1' are arranged across wedge members 2 and 2'. The electric signal from a transmission part 5 is supplied to the oscillator 1 through the solid-line position of a changeover switch (S) 6a and the propagation time T1 of the measured ultrasonic wave is stored in a storage circuit 8. Then, the propagation time T2 when the S6a is switched to a broken-line position is stored in a storage circuit 8. Further, the propagation time Tp of the ultrasonic wave propagated in the pipe 4 through a route lis measured by a measuring circuit 14. The flow rate calculated from the times T1 and T2 is corrected with the time Tp to measure the flow rate. Consequently, the flow rate is measured accurately even if the temperature of the fluid varies.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention relates to an ultrasonic flowmeter, and more specifically, it transmits and receives ultrasonic waves in the forward and reverse directions at a predetermined angle to the flow of fluid. The flow rate of the fluid is measured using a predetermined calculation formula from the difference ΔT between the respective propagation times when The present invention relates to an ultrasonic flow needle.

[Conventional technology]

Regarding such an ultrasonic flowmeter, the applicant has already proposed the following (Japanese Patent Application No. 58-204886).

FIG. 4 is a configuration diagram showing a proposed ultrasonic flowmeter (hereinafter referred to as a conventional example).

In this example, ultrasonic transducers 1 and 1' are connected to wedge member 2.
and 2' as shown in the figure, and the wedge members 2 and 2' allow the ultrasonic waves emitted from the 10,000 transducers to cross the tube through which the fluid 6 flows at a predetermined angle θ, and are reflected on the inner wall of the tube 4. They are installed on the outside of the tube 4 in a manner that they are lined up approximately on the same line so that they can be received by the other transducer after the
As a result, the ultrasonic transducer 1. Wedge member 2. Inner wall of tube 4, fluid 6. The inner wall of the tube 4, the wedge member 2' and the ultrasonic transducer 1' are acoustically coupled to each other.

That is, the ultrasonic transducer 1 converts an electric signal inputted from the transmitting section 5 through the changeover switch section 6a located at the solid line position into an ultrasonic wave, and oscillates it toward the other ultrasonic transducer 1'. do. The transducer 1' converts the received ultrasonic waves into electrical signals and outputs them. The reception and time measurement circuit 7 measures the propagation time T1 of the ultrasonic wave by combining the transmission signal from the transmitting section 5 and the reception signal from the transducer 1' received via the changeover switch section 6b located at the solid line position. do. This measured time T1 is given to the storage circuit 8 via the changeover switch section 6C located at the solid line position and is stored. Next, switch 6a
, 6b and 6C to the dashed line position, and vibrator 1'
By setting 1 to the transmitting side and 1 to the receiving side, ultrasonic waves are emitted and received in the opposite direction to the above, the propagation time T2 of the ultrasonic waves at this time is measured, and one of the memory circuits 9 is stored. Make me remember.

By the way, the ultrasonic propagation time T1 in the forward direction of the flow from the transducers 1 to 1' and the ultrasonic propagation time T2 in the reverse direction from the transducers 1' to 1 are the propagation times in the fluid, t,... If i2 is the propagation time in the wedge member or pipe wall other than the fluid, then it can be expressed by the following equation.

T 1=t 1+τ・・・・・・
・(1) T2 = t2+τ ・・
(2) Therefore, the propagation time difference ΔT can be calculated as follows.

ΔT −T2−T.

-(10τ) -(1,10τ) -12-1,...(5) Now, calculate the inner diameter of the tube 4 and set the sound velocity (propagation speed of ultrasonic waves) in the fluid to exceed C1. It is known that the above propagation time t1 + t2 h is generally expressed as the following equation, where the incident angle of the sound wave is θ and the flow velocity in the pipe is iV.

Therefore, ΔT is as follows.

Comparing the sound velocity C in the fluid and the flow velocity in the pipe, if the fluid is water, C is generally 1.000 to 1.600.
m, /S, while V is less than jom/El. Therefore, C">>V"sin"θ, and ΔT can be expressed as follows (Modern 1).

If the ultrasonic sound speed C in the fluid is constant, sin θ/C"
The amount of CO5θ is constant, and ΔT is proportional to the flow rate ■.

Therefore, by measuring ΔT, it is possible to measure the flow velocity V and the flow rate having a predetermined proportional relationship thereto.

By the way, in the above equation (7), when the sound speed C of the fluid does not change, the relationship ΔTαV holds true, but the sound speed C in the fluid changes as the temperature or pressure of the fluid changes. Further, as the sound speed C changes, the angle θ also changes according to Snell's law regarding reflection and refraction. Therefore, when the sound speed C changes, an error occurs in the measured value of the flow velocity V. In particular, when the temperature of the fluid changes from room temperature to high temperature (approximately 3aa°C) or when the thickness of the pipe is large, the influence of changes in the sound speed C becomes large and the measurement error becomes large. Therefore, the above equation (7) Transform as shown below.

Now, assuming that the fluid is stationary (V-0), from equations (4) and (5) above, we get 1. =12. Therefore, TI = T2 ""r.

From equations (1) and (2) above, we get, and by transforming this, we obtain. Substituting equation (11) into equation (7), we get
5ia2θ −−(T o−7 doors・■ ・・・・・・(12), and the following is obtained. Here, when the fluid is flowing, To can be approximately obtained as ( Equation 13) also holds true when V←0.In other words, in Equation (13), apart from ΔT and 'ro, if the angles θ and τ can be measured, the flow velocity V can be determined using a predetermined calculation device. However, it is not necessarily easy to independently measure this angle θ and the propagation time τ in parts other than the fluid.

However, To and 1/5in2θ and 1/(su
2θ·(To−τ)1] as shown in FIGS. 5 and 6, respectively, and it has been confirmed that this holds regardless of conditions such as temperature and pressure. Therefore, as shown in FIG. 4, the calculation unit 10 calculates the propagation time difference Δ
While calculating T, the average propagation time To is calculated in the calculation unit 11, and from this calculation 11LTo, the value of 1/(sia2θ・(To−Di)1) is calculated using a function generator, ROM, etc.
In the calculation unit 121C, this [! After multiplying ΔT by ΔT, the calculation unit 13 takes into account a predetermined scale factor (conversion coefficient), thereby determining the fluid flow velocity ■ or the flow rate Q.

[Problem that the invention seeks to solve]

The conventional method as described above also has the following problems.

In other words, the propagation speed C of ultrasonic waves in water is approximately 70°C when the water temperature is approximately 70°C.
The speed of sound C is fastest when the water temperature is higher (or lower) than that, as shown in Figure 7. Therefore, the propagation time T1
*T2 and average propagation time To are minimum at a water temperature of around 70°C. Therefore, if the water temperature of the fluid is determined with the pressure of the fluid constant, the propagation time To can be determined uniquely, but conversely, even if the average propagation time To is determined, the corresponding water temperature is Since there are two locations as shown in a and b in Figure 8, the water temperature cannot be uniquely determined. In other words, when correcting the sound speed C using the characteristic curves shown in FIGS. 5 and 6 as described above, the area (the R in Figure 5
1 and R2 in FIG. 6), the problem remains that it is not possible to determine which value should be used for correction. This becomes an obstacle when using the ultrasonic flowmeter in a wide range from room temperature to high temperature (approximately 300° C.), so it is desirable to take appropriate precautions.

[Means and actions for solving the problem] Since the sound speed of a fluid changes depending on the temperature, a means is provided to indirectly determine the temperature of the fluid from the propagation time of the ultrasonic wave in the pipe material.
By selecting the output of the sound velocity correction circuit based on this temperature information, the flow velocity and flow rate can be accurately measured even when the fluid temperature changes from room temperature to high temperature (approximately 300° C.).

〔Example〕

FIG. 1 is a block diagram showing an embodiment of the present invention, and the same parts as in FIG. 5 are designated by the same reference numerals.

As is clear from FIG. 1, this embodiment is characterized in that it is provided with a measuring circuit 14 for measuring the propagation time Tp of the ultrasonic waves propagating through the tube 4 along the path t as shown. In this case, there is no need to newly provide a wedge or an ultrasonic transducer, and the propagation time T-' of the ultrasonic signal propagating through the pipe can be determined by using the existing ones as they are. It should be noted that such ultrasonic signals have hitherto been processed as noise, but in this case they will be actively utilized. Further, the measurement of the propagation time T can be omitted by being performed by the reception and time measurement circuit 7. - The pipe material, vibrator 4, is made of PVC instead of iron, and the sound velocity C3 in the iron material is as shown in Figure 2.
It is known that the temperature decreases as the temperature increases. Since the speed of sound in this tube is not affected by changes in pressure, the propagation time T of the ultrasonic wave in the tube.

By measuring the sound speed, the speed of sound can be determined, and from this speed of sound, it is possible to uniquely determine the temperature having the relationship shown in FIG. If the temperature is known in this way, it can be determined which of the correction curves ①~@, @~θ, Φ~G, and θ~■ should be used for the correction curves shown in FIGS. 5 and 6. For example, if the fluid temperature is in the range of 0 to 70°C,
o, eb~θ is also (9
The curves ~θ and e~■ will be used, respectively.

Note that the characteristics shown in Figure 5 or 6 can be used as a function generator or as a semi-fixed memo! J(FLOM) or the like, it can be easily extracted by making these outputs selectable as a function of temperature and average propagation time To.

In this way, by measuring the propagation time Tp of the ultrasonic waves propagating in the pipe material, it is possible to determine the temperature of the fluid without installing a new element for fluid temperature measurement. Even if the speed of sound changes due to the
Flow velocity and flow-3k can be measured correctly.

In the above, reflection of ultrasonic waves is used, but the following method is also possible.

FIG. 3 is a block diagram showing another embodiment of the present invention. This system consists of two systems (A,
This is an example of measuring the so-called two survey lines set up in Block B). It is basically the same as shown in Figure 1, but each group (
Average value calculation unit 15 that averages the outputs of the B7' locks
By providing this system, more accurate measurement is possible, and in some cases, another system may be added. The measurement of the propagation time Tp in this case is carried out between the transducers 1a and 1b or 1a/1b', and is the same as that in FIG. 1 except for these points, so further explanation will be omitted.

〔effect〕

According to this invention, the following advantages or effects can be expected.

1) A method of measuring temperature and pressure with separate sensors and correcting them may be considered, but in this case, an error occurs due to a difference in detection time, and the error becomes particularly large in response to a sudden temperature change. In contrast, in this invention, the propagation time difference ΔT, which is the basis of the flow rate, and the average propagation time TO, which is the basis for correction.
and the propagation time Tr) in the tube material are always measured simultaneously, so no error occurs due to a difference in detection time.

2) It is possible to measure the temperature of the fluid without having to take the trouble to provide a thermometer.

5) Pressure signals can be extracted, although the accuracy cannot be expected to be very high.

4) In another embodiment of the present invention, by performing two-line measurement as shown in the embodiment, it is possible to reduce the measurement error due to the uneven flow of the fluid in the pipe.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of this invention. Fig. 2 is a graph showing the relationship between fluid temperature and sound velocity in iron. Fig. 3 is a block diagram showing another embodiment of this invention. Fig. 4. is a configuration diagram showing a conventional example of an ultrasonic flowmeter, and Fig. 5 shows the average propagation time To and 1
/sin 2θ. Figure 6 is a graph showing the relationship between average propagation time TO and correction coefficient. Figure 7 is a graph showing the relationship between water temperature and underwater sound velocity. Figure 8 is water temperature and average. A graph showing the relationship with the propagation time To is shown. Code explanation 1.1' + iat 1a', 1b + jb'
"..." Ultrasonic transducer, 2 + 2' r 2a r
2a', 2b, 2b'... Wedge member, 3... Fluid, 4... Tube material () (Eve), 5... Transmitting part, 6a j 6b, 6C・
. . . Selector switch section, 7 . . . Reception and time measurement section, 8, 9 . . . Memory circuit, 10 . . .
... Time difference (ΔT) calculation section, 11 ... Average propagation time (TO) calculation section, 12 ... Sound speed correction calculation section, 13 ... Scale factor calculation section, 14・・・
... Pipe material propagation time measurement circuit, 15 ... Average value calculation section. M1 Figure 22 Figure 3 Figure 4 Figure @ 5 Figure 8 Mizuki

Claims (1)

[Claims] By transmitting and receiving ultrasonic waves in the forward and reverse directions at a predetermined angle to the fluid flow, the difference in propagation time, the average propagation time of both, and a correction amount that has a predetermined functional relationship with the average propagation time This is an ultrasonic flowmeter that calculates the flow rate by correcting the flow rate calculated using the propagation time difference with the correction amount, and measures the flow rate based on the propagation time of ultrasonic waves that propagate without passing through the flow of the fluid. 1. An ultrasonic flowmeter comprising a temperature measuring means for measuring the temperature of the ultrasonic flowmeter, the correction amount being determined based on the temperature, and the flow rate being measured.